1. Field of the Invention
The present invention relates to a method for producing a proton-conducting, structured electrolyte membrane, especially for a fuel cell.
2. Description of the Background Art
Batteries and accumulators can be replaced by fuel cells. These typically have a hydrogen storage system, a first electrode acting as the anode, a second electrode acting as the cathode, and a membrane which is located between the electrodes and is connected to the hydrogen storage system. The membrane is permeable to protons and impermeable to hydrogen. In micro fuel cells, a film, usually obtainable commercially under the name DuPont™ Nafion® PFSA membrane, is used as the electrolyte membrane. The electrolyte membrane contains chemically stabilized sulfonic acid groups, which enable a high ionic conductivity.
In a method known from the conventional art, during the production of the fuel cell the film is structured by cutting and made into the required shape. The film is then arranged between the electrodes. Typically, a plurality of such fuel cells is stacked one above the other and connected in series. The film has the disadvantage, however, that it enables only limited miniaturization of the fuel cell, because the structured film is still difficult to handle if its dimensions are small. It is disadvantageous in addition that tolerances, which make the miniaturization of the fuel cell difficult, occur during the trimming of the film.
In T. Pichonat et al., “A new protein-conducting porous silicon membrane for small fuel cells”, Chemical Engineering Journal 101 (2004), pages 107-111, further, a method for producing a structured electrolyte membrane is disclosed, in which a silicon wafer is coated on both sides by a metallic layer applied by sputtering. A mask of a photoresist is then applied to this layer and next at the places where no photoresist is arranged, the wall thickness of the wafer is reduced by double-sided etching of the silicon, to form an open-pore silicon membrane, which has a surface of about 3 mm×3 mm. The silicon membrane is then filled with a Nafion® solution and next the solvent contained therein is evaporated so that only the Nafion® remains in the pores. This method also enables only limited miniaturization of the membrane, because the charging of the silicon membrane with the Nafion® solution is difficult with small membrane dimensions.